1. Field of the Invention
The present invention relates to a fine organic silicone particle for latent electrostatic image developing toners, an external additive for toners, a latent electrostatic image developing toner, a two-component developer, and a developing device using them.
2. Description of the Related Art
It has been proposed that the use of fine inorganic particles with large diameters is effective in improving toner's developability, transferability and cleanability, as well as in preventing embedment of external additive in toner particles that is caused by various stresses on the toner particles. Also disclosed is a technology in which organic fine particles that are 50 nm to 200 nm in diameter are added to toner in order to provide an effective spacer function. When an external additive is mixed with toner using a mixer, it is necessary to dissociate aggregates of the external additive and toner for deposition of the external additive onto the toner surface. However, this process causes a situation where some particles of external additive occasionally remains free without adhering to the toner surface, or where some particles of external additive bonded to the toner surface to some degree are detached from the toner surface by stress, a friction, etc. in the developing device. The above free external additive is often recognized to move to the photoconductor with toner at the time of toner development on a photoconductor surface, remaining on the photoconductor surface even after transfer of the developed image and adhering to the photoconductor surface without be removed by cleaning process. When free external additive particles are deposited onto the photoconductor surface, they become a frequent cause of image quality defect on a copy (filming, etc.) or scratches on the photoconductor, thereby reducing the lifetime of the photoconductor. Further this also causes contamination of the copier when the free external additive drops out of the developing device upon development. Moreover, the free external additive adheres to carrier surface in a developer and inhibits transportation of electric charges between toner and carrier, which may result in reduced toner charge amount.
Japanese Patent Application Laid-Open (JP-A) No. 06-266152 discloses using as external additives fine inorganic particles having a volume-average particle diameter of 30 nm to 150 nm and organic fine particles having a volume-average particle diameter of 50 nm to 200 nm made of high-melting point resin with a flow-starting temperature of 200° C. or more in order to reduce the degree of embedment of external additive into toner particles. However, it is technically difficult to effect uniform surface treatment on such two different types of fine particles, and it is also difficult to strike a balance between prevention of embedment and prevention of detachment of external additive because the two external additives have different affinities for the toner binder. Meanwhile, JP-A No. 07-28276 discloses using as external additives small diameter-inorganic particles in combination with large diameter-inorganic particles, such as particles of silica, titanic oxide or alumina that are hydrophobized by treatment with a silane coupling agent. However, sufficient external additive functions have not yet been achieved by this technology, which is due in part to the fact that external additive particles generally offer a broad particle size distribution. JP-A No. 09-319134 discloses adding, among inorganic external additives with a relatively large particle diameter and organic external additives with a relatively small particle diameter, organic and inorganic external additives each having a number-average particle diameter of 0.05 μm to 0.5 μm in such amounts that the toner turbidity is 10 to 50. However, this technique is not directly associated with prevention of embedment of external additive in toner particles and with prevention of detachment of the external additive from the toner particles. Furthermore, JP-A No. 10-312089 discloses, in order to increase the toner charge amount, using as an external additive silica that is hydrophobized by treatment with a silicone oil and that has a primary particle average diameter of 30 nm to 100 nm in combination with a zinc salt of benzylic acid derivative as a charge controlling agent. This technique is not also directly associated with prevention of embedment of external additive in toner particles and prevention of detachment of the external additive from the toner particles.